First-principles Investigations On The Electronic Structures And Transport Properties Of InAs-based Nanosystems

For years the exponential field-effect transistors(FET) semiconductors based on conventional Si-materials and electronics industries have been fully increased, highly completing great density of Si-FET in the integrated circuits. However, Si-FET scaling is now reaching its limit with decreasing the scale of nanoelectronic device. Serial issues have been taken place, such as, heat production, low carriers mobilities, and small ION/IOFF ratio etc., threatening the microelectronics revolution. Attention is turning to introduce a new material, meeting the high performance in modern nanoelectronic devices. III-V semiconductors, such as, In As and Ga Sb, have more excellent physics and carriers mobilities than Si, overcoming the obstruction in the Si-based nanodevices. Because of their obvious properties, In As and Ga Sb are the attractive material for high performance and high speed nanoelectronic devices. In this dissertation, we have used first principles method to systematically investigate the quantum confinement effect on the electronic structures and transport properties of In As nanowires, the effects of the strain and chemical composition on the electronic properties on the Ga Sb/In As core-shell nanowires and carriers mobilities, and the optical absorption properties of In As composited with two-dimensional nanostructures. Some interesting and meaningful results have been obtained.Firstly, we have used first-principles methods to systematically investigate the quantum confinement and surface effects on the electronic properties of zinc-blende and wurtzite In As nanowires with different orientations and diameters, analyzing the mechanism of the effects on the electronic properties, and compared the electronic structures and transport properties of nanowires before and after pseudo-hydrogen passivation explaining the reasons for improving the transport properties of passivated nanowires. The results show that the calculated band gaps of nanowires are dependent on the nanowires diameters, decreasing with the increases in diameters. The increase in the band gap is proposed relationship of αβ DEg=Δ/(D represents diameter). The effect of quantum confinement on the conduction bands is greater than on the valence bands, leading to non-linear variation between the band gap and the diameters. The calculated carrier effective masses are also dependent on the NW diameter. The effective masses of [111] ZB NWs are smaller than the hole effective masses when the NW diameter is ≥26 ?, increasing the electronic mobilities. The gap-states are removed by passivating the dangling bonds of surface atoms, decreasing the electronic densities at the nanowires surface. The carrier effective masses and mobilities can be adjusted by passivating the surface dangling bonds.Secondly, the effects of the chemical composition and strain on the electronic properties of [111] zinc-blende(ZB) and [0001] wurtzite(WZ) Ga Sb/In As core-shell nanowires with different core diameters and shell thicknesses are studied using first-principles methods. The band structures of the [111] ZB Ga Sb/In As core-shell NWs underwent a noticeable type-I/II band alignment transition, associated with a direct-to-indirect band gap transition under a compressive uniaxial strain. The band structures of the [0001] WZ Ga Sb/In As core-shell NWs preserved the direct band gap under either compressive or tensile uniaxial strains. In addition, the band gaps and the effective masses of the carriers could be tuned by their composition. For the core-shell NWs with a fixed Ga Sb-core size, the band gaps decreased linearly with an increasing In As-shell thickness. It indicates there has a threshold In As-shell thickness that leading to a band structure characteristic transition from semiconductor to semimetallic. For the [111] ZB Ga Sb/In As core-shell NWs, the calculated effective masses indicated that the transport properties could be changed from hole-dominated conduction to electron-dominated conduction by changing the In As-shell thickness.Thirdly, we investigated the electronic properties of Zn doping in Ga Sb/In As core-shell nanowire and in two-dimensional(2D) Ga Sb/In As heterogeneous slabs, and calculated the electron and hole mobilities using deformation potential theory. The results show that for ZB [111] Ga Sb/In As core-shell nanowire the Zn p-type doped In As shell donates free holes to the non-doped Ga Sb core nanowire without activation energy, significantly increasing the hole density and mobility of nanowire. The carries mobilities of the non-doped and Zn-doped Ga Sb/In As core-shell NWs have been estimated based on the deformation potential theory. We find the Ga Sb hole carrier mobility has been increased by 1044 cm2/V·s, a remote p-type doping has been realized in Ga Sb core. In order to explore the key factor in achieving remotely p-type doping, we investigated the behavior of Zn doping in the Ga Sb/In As heterogeneous slabs with different surface planes. From the calculated results, we infers that remote p-type doping can be achieved in the Ga Sb/In As core-shell NWs that with(110) side facets and the(111) side facets with As atoms termination, such as ZB [001] and WZ [0001] Ga Sb/In As core-shell NWs.Finally, we systematically studied the electronic structure, charge distribution, and optical absorption characteristics of Graphene/In As(111) surface and Mo S2/In As(111) surface nanocomposite structure. For the Graphene/In As(111) surface nanocomposite structures, when graphene was composited on the In-terminated In As(111) surface, the interactions between the surface would prompt charge from In As(111) surface to graphene, forming the polarized field electric field and electron-hole pairs between the interface, which would enhance the adsorption of red, however, the when graphene was composited on the As-terminated /In As(111) surface, the obvious charge transfer and enhanced adsorption of light can not been found. In addition, the Dirac point of graphene is shifted, associated with the change of electrons in electronic of graphene after its adsorption on In As(111) surface. After the adsorption of Mo S2 on In As(111) surface, large amounts of heat are released, forming chemical bonds. Meanwhile, the large charges have been transferred from In As(111) surface to Mo S2, electrons and holes are found in Mo S2 and In As(111) surface, respectively. The nanocomposites of Mo S2/In As(111) surface are more stable than graphene/In As(111) surface nanocomposites. The light adsorption is more obvious for Mo S2/In As(111) surface nanocomposites than graphene/In As(111) surface nanocomposites. Our results may be helpful for designing high-performance electronic devices.